Nitrogen as a greenhouse gas
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Nitrogen and Greenhouse Gas Emissions: Key Mechanisms
Nitrogen, while not a greenhouse gas itself, plays a major role in the emission of greenhouse gases (GHGs) from soils and agricultural systems. The main GHGs influenced by nitrogen are carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). Nitrogen addition, through fertilizers or atmospheric deposition, can increase the emissions of these gases by altering soil microbial activity and nutrient cycles 15679.
Nitrogen Addition and Global Warming Potential
Studies show that adding nitrogen to soils generally increases the combined global warming potential (CGWP) of CO₂, CH₄, and N₂O emissions. The largest contribution to this increase comes from CO₂, followed by N₂O, with CH₄ playing a smaller role. Wetlands and permafrost peatlands are especially sensitive, showing the highest increases in GHG emissions with nitrogen addition 19. In permafrost peatlands, nitrogen addition boosts the abundance of soil microbes that produce GHGs, further increasing emissions .
Nitrogen Fertilizer Use and Agricultural Emissions
Nitrogen fertilizers are a major source of GHG emissions in agriculture, accounting for about half of total emissions from crop cultivation. The production and use of these fertilizers contribute significantly to national and global GHG inventories 248. In China, for example, nitrogen management is linked to over 13% of the country’s total GHG emissions, with fertilizer use efficiency being less than 30% for cash crops, leading to high nitrogen surplus and emissions 28.
Effects of Nitrogen on Individual Greenhouse Gases
- Nitrous Oxide (N₂O): Nitrogen addition consistently increases N₂O emissions due to enhanced microbial nitrification and denitrification in soils. This effect is observed across various ecosystems, including drylands, alpine steppes, and peatlands 5679.
- Methane (CH₄): Nitrogen addition often reduces the soil’s ability to absorb methane, especially at intermediate fertilization levels, leading to higher net CH₄ emissions 579.
- Carbon Dioxide (CO₂): The impact of nitrogen on CO₂ emissions is more variable. In some cases, nitrogen addition increases CO₂ efflux from soils, while in others, it has little effect or even stimulates carbon sequestration, depending on the ecosystem and management practices 1356.
Nitrogen Management Strategies for Emission Reduction
Improving nitrogen use efficiency, balancing fertilizer application, better manure management, and reducing food loss and waste are effective strategies to reduce nitrogen-related GHG emissions. Combining these approaches with decarbonization of fertilizer production could cut fertilizer-related GHG emissions by up to one-fifth by 2050 24. In constructed wetlands, the presence of aquatic plants can help control GHG emissions by supporting beneficial microbial processes and acting as carbon sinks .
Interactions with Climate Change and Ecosystem Responses
The effects of nitrogen on GHG emissions are influenced by climate factors such as temperature and precipitation. Warmer temperatures and higher nitrogen addition rates tend to increase GHG emissions, while higher precipitation can reduce them 16. The balance between carbon sequestration and GHG emissions is complex, and in some cases, the benefits of increased carbon storage are offset by higher N₂O emissions, resulting in a net warming effect 35.
Conclusion
Nitrogen, through its influence on soil processes and microbial activity, is a key driver of greenhouse gas emissions in terrestrial ecosystems. Managing nitrogen inputs more efficiently and adopting integrated strategies can significantly reduce the climate impact of agriculture and other land uses. Understanding the interactions between nitrogen, greenhouse gases, and climate is essential for developing effective mitigation policies.
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